The invention relates to a grapple apparatus for grasping and lifting loads, and the method of operation of the apparatus, and is particularly adapted for handling bulk loads such as logs and logging debris associated with industrial forest harvesting operations.
Logging grapples have been used for many years for lifting fallen logs, and for moving the logs to a staging area for later transportation. Such grapples were designed generally to retrieve single logs and usually had a single pair of opposed curved grapple arms which were hinged for rotation towards each other to grasp the log therebetween. Such grapples were often carried on cable systems, and some required a closing cable for drawing the arms together, and sometimes a separate opening cable for releasing the arms. Nowadays, some grapples can be suspended by a cable from a helicopter, and difficulties can arise if separate cables are required to actuate the arms of the grapple for grasping and releasing the load. If a separate cable is required to actuate the grapple, an additional grapple operator is required in the helicopter or else the helicopter pilot can be overworked. Alternatively, if actuation of the grapple requires direct manual intervention on the ground, an operator is required on the ground which increases labor costs and safety of that operator. Consequently, it is desirable to eliminate the prior art cables used to actuate the grapple. As an alternative to a separate cable or cables for actuating the grapple, other actuators such as hydraulic cylinders have been used to generate forces for moving the grapple arms. These require hydraulic fluid hoses and fluid pressurizing systems which increased complexity considerably.
When releasing a load from a prior art grapple, a release latch is actuated and this often requires some considerable force to overcome friction generated by load carried by the grapple acting on the latch. In such circumstances, when the load is released, it tends to be released suddenly, causing a shock load on the grapple and supporting cable, which can be hazardous if the grapple is carried on a helicopter.
Grapples have been used for gasping other loads, for example, U.S. Pat. No. 1,151,052 (Sales) discloses a hay lifting grapple having a pair of opposed curved arms that are rotatably mounted to a frame supported by a derrick. The lower ends of the curved arms carry a pair of opposed curved forks which are latched to the arms for gasping material therebetween. A separate cable is required to unlatch the forks to release the load. U.S. Pat. No. 1,003,352 (Gaussiran) discloses a grapple for handling large loads and is provided with two sets of curved arms mounted on a common main hinge, each set having a plurality of arms which are spaced laterally apart along the hinge on one side thereof to grasp elongated loads. The arms of each set are connected together for concurrent rotation relative to each other, and the sets of arms are controlled by a rope passing around a pair of pulleys coupled to each arm. U.S. Pat. No. 572,490 (Lewis) and U.S. Pat. 52,134 (Buckman) both disclose hay forks which are suspended from a rope and are actuated by a separate control rope. Buckman has a pair of lower rake portions, each of which is hinged to a respective main arm for rotation thereabouts, and is coupled to an opposite arm by a respective rigid link so that opening of the main arms simultaneously actuates the rake portions.
To the inventor's knowledge, most grapples used in prior art cable supported logging systems are inappropriate for helicopter use due to the complexity of cable or hydraulic actuation of the grapple, and to the said shock loads generated during opening of the grapple to release the load. Other prior art grapples require an operator close by to manually operate structure on the grapple, which would be inappropriate for helicopter carried grapples used in logging operations.